Digital magnetic recording stores digital data by modulating a magnetic flux pattern in a magnetic medium. During the storing process, an electric current in a write head is modulated based on the digital data to be written. The head is positioned over magnetic material in the shape of a circular disk which rotates rapidly. The electric current in the write head, in turn, modulates the magnetic flux pattern in the medium. The medium chosen is such that the flux pattern is retained in the medium after the electric current is turned off in the write head, thus providing data storage.
Data is usually written in the medium in concentric circles called tracks, which are further divided into sectors, with each sector storing a fixed quantity of information. Data and supporting bit patterns required for control and synchronization when reading the data are written into the tracks.
During a read process, a read head is positioned over the medium following the tracks, but now the magnetic flux pattern in the medium induces a current in the read head. This current is then processed to recover the written data. The reading of the signals from the read head uses an analog signal path including filtering, amplification, and timing acquisition stages. The read process begins with the reading of synchronization bit patterns, that contain preamble symbols.
Limitations in the analog portion of the timing acquisition and read signal processing path tend to increase the preamble symbol format overhead in order to achieve good performance in reading magnetically stored digital information.